The present invention relates to a camshaft driving arrangement for a double overhead camshaft (DOHC) engine having two camshafts for opening and closing suction and exhaust valves at each of cylinder heads.
Japanese Patent Publication No. 59-74312 (=U.S. Pat. No. 4,553,473) discloses a camshaft driving arrangement of the prior art as shown in FIG. 6.
Referring to FIG. 6, there is shown a so-called V-type DOHC engine in which a cylinder block 1 includes two cylinder banks 1A and 1B angularly disposed to each other. One 1A of the two cylinder banks has a plurality of cylinders displaced along the axis of a crankshaft 2 from a plurality of cylinders of the other bank 1B. There is provided a sprocket 3 at theend of the crankshaft 2 rotatably mounted to the cylinder block 1. Rotatably mounted to each of cylinder banks 1A and 1B are an intake camshaft 6 for opening and closing intake valves 5 and an exhaust camshaft 8 for opening and closing exhaust valves 7. Two idler gears 11 are rotatably mounted to the cylinder heads 4A and 4B, respectively. Each of the idler gears 11 has a large diameter gear 11A and a small diameter gear 11B. Fixdely mounted to the end of each of the camshafts 6 and 8 is a sprocket 9. Rotation of the crankshaft 2 is transmitted to the large gears 11A of the idler gears 11 through a rubber timing belt 10, causing rotation of the small gears 11B. Subsequently, the rotation of each of the small gears 11B is transmitted to the adjacent sprockets 9 through a chain 12. As a result, the intake camshafts 6 and the exhaust camshafts 8 are rotated synchronously, opening and closing the intake and exhaust valves 5 and 7. A tensioner 13 is used for adjusting the tension of the timing belt 10, and an idler gear 14 for stabilizing or ensuring an engagement of the timing belt 10.
With such conventional camshaft driving arrangement, case covers (not shown) for the timing belt 10 and the chains 12 are mounted to an engine body in overlapping the end portions of the case covers each other, and the timing belt 10 is designed to be large in width. This increases the overall length of the engine and the dimension of the case covers, and decreases the assembling efficiency of the timing belt 10 and the chain 12. Additionally, the tensioner 13 and the idler gear 14 are mounted between the two idler gears 11 so that the middle portion defined by the timing belt 10 cannot be used for installing engine's accessories.
An object of the present invention is to provide a camshaft driving arrangement which makes much contribution to reduced overall length and increased space for installing engine's accessories.